In industrial installations, use is generally made for monitoring the installation of measurement sensors supplying information about various parameters representing the running of a process within the industrial installation.
Customarily, industrial installations using at least one fluid involved in the process performed comprise sensors for measuring thermodynamic parameters of the fluid, such as pressure sensors, flow sensors, temperature sensors or fluid level sensors. In particular, in nuclear power stations, use is made of numerous sensors which measure and monitor thermodynamic parameters of a heat exchange fluid of the nuclear power station.
Certain sensors are used only when the nuclear power station experiences an incident or when an accident occurs, or alternatively, during phases of limited duration while the power station is operating.
Such sensors are associated with a measurement sequence that allows an electric signal supplied by the measurement sensor to be collected and processed.
When it is necessary to have a sensor and its measurement sequence available in a situation where an incident or an accident has occurred, information is not generally available that will make it possible to guarantee that the sensor and its measurement sequence are actually available to supply the necessary information. This is because the availability tests performed on the sensors and their measurement sequence may have been carried out in a period very far removed, in terms of time, from the time when use of the sensor becomes necessary. For example, the situation may arise where the availability tests on the sensors of a nuclear power station were performed before the power station was started up, and the use of the sensors if an incident or accident occurs arises only a very long time after the power station has been started up, for example a year or more after start-up.
In certain situations it is absolutely essential to have sensors and their measurement sequence available, even though it is not possible to obtain information regarding the availability of these sensors and measurement sequences while the installation is operating.
In certain industrial installations, particularly in nuclear power stations, availability tests are carried out periodically on the monitoring sensor measurement sequences, but these tests relate only to the electrical part of the measurement sequence and do not allow the influence on the sensor of a thermodynamic parameter of a fluid present inside the industrial installation to be verified. It is therefore not possible to be sure that the sensors and their measurement sequence are capable, at a given moment, of supplying the information that is essential if the industrial installation experiences abnormal operating conditions.
As a result, and in particular in the case of nuclear power stations, it has proved to be extremely desirable to have a method for checking the availability of sensors on the nuclear power station in operation that can be carried out at any time.
Hitherto such a method for checking sensors and in particular for checking sensors that measure and monitor thermodynamic parameters of a fluid in a nuclear power station while it is operating has not been available.
In order to make functional checks on the sensor itself, independently of its measurement sequence, tests are carried out on test benches, after the sensor has been removed from the installation. Such a method does not allow the sensor itself and its measurement sequence to be checked simultaneously.
In U.S. Pat. No. 4,825,685 the pressure of a fluid in a chamber of a sensor in contact with a sensitive element of the sensor is modulated using a piezoelectric element placed in the chamber of the sensor. The modulating of the pressure, in order to check the sensor, entails energizing the piezoelectric element with an electric current, and this may present disadvantages in certain applications.